In recent years, there have been proposals to allow multiple tiers of users to share access to radio frequency spectrum that is presently unlicensed or only used by a current licensee on an as-needed basis. A present proposal would authorize a set of channels within an available range of frequencies in a shared radio frequency spectrum model. In this shared radio frequency spectrum model, a set of channels may be at any frequency within the recently made available larger frequency band. In other words, for example, a license may be purchased for a 10 kHz channel in the frequency range of 20 MHz-22 MHz. Under a proposed licensing arrangement, any device would be allowed to operate within the 20-22 MHz range, but only on a temporarily assigned 10 kHz channel within the range. This new licensing proposal is like a general seating arrangement in a baseball stadium, where an outfield general seating ticket is purchased and the ticket holder is seated anywhere the usher directs so long as it is in the outfield bleachers section of the baseball stadium, as opposed to purchasing a designated specific seat ahead of time. In other words, the user does not choose a specific seat in a general seating arrangement, and similarly, a user in the shared access radio frequency system would not have a statically assigned channel or set of channels at a specific frequency, but instead would have a potentially different channel assigned from time to time. In these Shared Access Systems (SAS), a SAS Manager is employed to allocate channels among the various users. The SAS Manager is typically an external controller (or network of controllers or servers) located at a remote location where Internet Protocol communications (IP) are used to link the local device, Access Point, or Base Station device to the SAS Manager. This SAS arrangement is quite different than present exclusive use licenses, where fixed, defined portions of frequency spectrum in a fixed area or jurisdiction are assigned for a fixed term to a licensee.
An initial proposal establishes a tiered priority access system for the SAS. The first tier (Tier 1) is reserved Government and military incumbent operations who are the highest priority and the highest power-emitting users. The next tier (Tier 2) may be Priority Access/Commercial Wireless Network Providers (e.g. Verizon®, AT&T® and the like), who are proposed to have a mid-level priority and may have medium power emission levels, and the third tier (Tier 3), known as General Authorized Access (GAA) which would have the lowest priority and lowest power emission levels. The most extreme example of the dynamic range problem is a Tier 1 user that uses a radar air interface at very high power sharing a set of channels with a commercial wireless wide area network (WWAN) network, such as using the 4G Long Term Evolution (LTE) air interface at low powers commensurate with a small cell implementation. Because the radar system is operating at a very high power level, many channels of operation for the lower powered WWAN system may experience front end overload interference. This interference may affect the use of channels that are co-channel (i.e., share a portion of the same channel), adjacent channel, next adjacent channel, and any channel that is in the bandwidth of the receiver front end. This is because the high power signal of the radar may overload the front end (receiver's) low noise amplifier (LNA) and subsequent mixer stages before the later filtering in the receiver occurs (in order to select the actual reception channel). This is often termed front end ‘Blocking’ where a high power signal within the radio frequency bandwidth of the receiver front end degrades, desensitizes, or completely overwhelms reception of the desired low level signal. Because the radar system has a very high power amplifier and a very high gain, narrow beam width antenna, the area covered by the radar signals may be very large, precluding or excluding operation of the other lower powered systems over very wide areas. These exclusion zones not only prevent operation of the lower powered systems on the same channel, but also prevent operation on many other channels due to the front end overload condition, where the low power receiver LNA is driven past its linear operation point.
Hence a need exists for a system that minimizes the chances of blocking lower power devices by segregating the frequency bands through the use of filtering and by secure control of this operation to prevent unauthorized users from interfering with authorized users.